? RE: Duals and Rear Discs on my Caprice - Chevy Impala SS Forum
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post #1 of 16 (permalink) Old 06-26-2001, 09:31 PM
FakeSS
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I just came across a smokin' deal - I got a 9C1 wiper arm w/ the air deflector. It only cost me $200.

What? You say I got ripped off? Well what if I told you they threw in a stock 9C1 dual exhaust (cat-back), tranny support, and a complete rear end (posi w/ discs - not sure of the ratio, but hey, for $200 who cares)?

I've had a set of stock Impala SS manifolds (which should bolt right up to my 305 heads) and cats sitting around for a while now. I understand that I'll have to fool with the frame some to get the support to fit correctly.

Anyway, here are my questions: I've read here in the past that there is another piece that I will need to mate the support to the tranny. What is it & does anyone have the part number? (Yes I know, I should do a search through past posts but my dial-up is soooooooo slooooowwwww.)

Also, for those of you who have converted from rear drums to discs - what should I be prepared for? Any brake lines/hoses that I need to have on hand? And will I be able to bleed the brakes properly after making a whole rear end swap (I'll most likely be doing this by myself) or would I be better off paying a shop to make the switch?

TIA
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post #2 of 16 (permalink) Old 06-26-2001, 09:52 PM
Mike454SS
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I believe the other tranny part you need Jay is the tailshaft from a 94-96 car.
post #3 of 16 (permalink) Old 06-27-2001, 02:47 PM
kdrolt
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<BLOCKQUOTE>quote:</font><HR>Originally posted by FakeSS:
... Also, for those of you who have converted from rear drums to discs - what should I be prepared for? Any brake lines/hoses that I need to have on hand? And will I be able to bleed the brakes properly after making a whole rear end swap (I'll most likely be doing this by myself) or would I be better off paying a shop to make the switch?
TIA
<HR></BLOCKQUOTE>

Get a 94-96 proportioning valve AND 94-96 9C1 master cylinder.

The rear discs require more fluid volume to operate the caliper pistons to full travel than rear drums, so you need the 9C1 master cylinder. Actually the Impala SS one should work too but I think the 94-96 9C1 master cylinder (from memory) has a larger piston diam so the brake feel is harder. Cops must like it harder... &lt;g&gt;

The proportioning valve, OTOH, can be from ANY 94-96 B platform car. You *will* be doing the proportioning mod to it (described on the IGBA website), so you will have the full rear brake capability.

I don't know about the emergency brake cable. The SS/9C1 rear end uses a drum-in-rotor-hat ebrake, that is cable actuated. The 93 and prior cars use the std rear drums themselves (or at least one shoe) as the ebrake, but I don't know if the cable connection is the same or not. So you might have to go with the 94-96 SS/9C1 ebrake cable; I don't know if it is different from the 94-96 rear drum cars or not. Dal could probably tell you by comparing p/ns. HTH. - Ken
 
post #4 of 16 (permalink) Old 06-27-2001, 04:33 PM
Mike454SS
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Ken, is the drum in hat e-brake setup the reason that the rear brakes squeak so badly if you try to engage the e-brake while moving? (I tried to see how long it would take to stop the car with it if my brakes went out, lets just say the E-brake is only useful for holding the car off of the tranny when its in park on a slanted surface).
post #5 of 16 (permalink) Old 06-27-2001, 06:28 PM
FakeSS
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Thanks guys! I appreciate the info.
post #6 of 16 (permalink) Old 06-27-2001, 07:37 PM
Sleeper
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Jay, the parking brake cable is different, but the brake lines are not. You should not have any trouble doing the swap by yourself. For the crossmember, you may not need the tailshaft itself, maybe only the trans mount. I am not sure on this, as I cannot remember exactly what my 91's tailshaft and mount looked like. Take a look at where your mount is before you buy a tailshaft assembly.

Axle ratio will be either a 3.08 or a 3.23. Easy to check by watching how many times the pinion rotates for 1 rotation of the axle shaft. Or, look for the stamping on the axle.

2LW : 3.08 open
2LX : 3.08 posi

2LY : 3.23 open
2LZ : 3.23 posi
post #7 of 16 (permalink) Old 06-28-2001, 10:15 AM
kdrolt
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<BLOCKQUOTE>quote:</font><HR>Originally posted by Mike454SS:
Ken, is the drum in hat e-brake setup the reason that the rear brakes squeak so badly if you try to engage the e-brake while moving? ....<HR></BLOCKQUOTE>

I don't know for sure, but from what you described, I'd say yes.

The emergency (rear drum) brake that sits within the hat of the rear rotor is TINY, and it doesn't get used much. The squeaky sound was probably from rust and brake lining abrasion. - Ken '94 9C1
post #8 of 16 (permalink) Old 06-29-2001, 08:57 AM
Navy Lifer
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For Ken Rolt--

Regarding the reason for the larger master cylinder on the 94-96 9C1 (1.25 on 9C1 vs 1.125 on Impala SS), I'm inclined to believe that the reason has nothing to do with the rear disc brakes, since they are the same on both vehicles.

It does, I believe, have to do with the greater piston travel on the front calipers, since the 9C1 uses a thicker pad, and the fluid displacement requirements at the point the 9C1 front pads (D614A) have worn to the same point that Impala pads (D614) would be screaming "replace me", the larger M/C would still have enough fluid-moving capability to finish off the extra .090" of pad on the 9C1 and keep the pedal within a reasonable (off the floor) travel range.

I do agree that a 1.25" M/C will (or SHOULD) give a firmer pedal on an Impala, but I don't think the police car engineers at GM were looking for a firmer pedal on the 9C1. I could be wrong, I will admit.

Let the discussion continue--show me how I'm wrong, Ken!
post #9 of 16 (permalink) Old 06-29-2001, 10:08 AM
kdrolt
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<BLOCKQUOTE>quote:</font><HR>Originally posted by Navy Lifer:
... Let the discussion continue--show me how I'm wrong, Ken!<HR></BLOCKQUOTE>

Hell no. I think you ARE right. [img]smile.gif[/img]
post #10 of 16 (permalink) Old 06-29-2001, 11:19 AM
kdrolt
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Navy Lifer then wrote to me offline and it adds to the further discussion so I'm posting it here:

<BLOCKQUOTE>quote:</font><HR> I've checked--93 9C1 (master cylinder diam) is 1.125", which I believe lends further support to myscenario. The only connection to the 94-96 cars is that the 93 car used the D614 pad, also on 94-96 Impala (RPO JB9). <HR></BLOCKQUOTE>

Then I'd say your idea, needing more MC swept volume to feed the longer throw 9C1 front discs is the correct ones.

Actually, I had written

<BLOCKQUOTE>quote:</font><HR> The rear [9C1] discs require more fluid volume to operate the caliper pistons to full travel than rear drums, so you need the 9C1 master cylinder.<HR></BLOCKQUOTE>

and that's still true. In addition to that, the front 9C1 calipers also demand more fluid because of the longer throw pads (as you reminded me), so I'll say it was for BOTH reasons.

To go any further with this, we'd have to compare the fluid demands for the disc/drum Caprice front calipers and rear drum wheel cylinders, and then compare the swept total volume at the wheels (from min wear to max wear) and as theroetically provided by the MC, against the WX3 with disc/disc and against the 9C1 with disc/disc.

That would be a neat exercise is sanity checking the work of the GM brake engineer(s).

Now if YOU want to look these up, by all means go ahead. &lt;vbg&gt; - Ken
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